Test meter for magnetos



Aug. 28, 1945. D F. MCCLELLAN ETAL 2,383,557 l TEST METER FOR MAGNETos I Filed Aug. 24;,1945

Patentedy Aug. 28, 1945 NT yprincipi,

TEST METER Fon MAGNE'ros s Donald F. McClellan and` Henry Cha'sen,

Boston, Mass.

Application Augustf24,1943serialN0.499,764 s r 1 claim. (ol. 1777-311) This invention relates to improvements in test -I meters used in adjusting the magnetos of aircraft, marine, motor vehicle and other vinternal Vcombustion engines which are equipped with magnetos for controlling the timing of the engine.

The principal purpose of the invention is to provide av simple, economicaland elicient test meter which will easilyI and accurately indicate the exact instant that the `breaker points of the magnetosf open and close, and which may be easily connected for testing without disturbing the electrical circuit of the magneto.

One object of theinvention is to provide a testing device which may be housed in a small, compact and easily transportable container, which may be quickly attached to the magneto by ordinary lead wiresfand which may be so connected that the timing of the engine may be tested and regulated while its ignition switch is in off position.

A further object is to provide a test meter which whill simultaneously indicate the timing relationship of both of a pair of magnetos with which aircraft engines are normally equipped, whereby the two magnetos may be accurately synchronized or adjusted for staggered operation, as required.

A recommended embodiment of our invention is shown in the accompanying drawing of a test meter adapted for testing a pair of magnetos, but it will be understood that the structural and electrical details of the apparatus herein illustrated and described may be varied to suit particular conditions without departing from the essence of this invention as defined in the appended claim` In the drawing,

Fig. 1 is a perspective view of the meter case, showing the dual meters, the switches of the respective meter circuits, and the jacks or terminals to which the leads to the magnetos are connected; and

Fig. 2 is a circuit diagram showing the relative arrangement of the electrical elements of the dual circuits when the testing device is connected to a pair of magnetos.

For dual operation, the meter case II contains a pair of batteries, indicated at l2 and I2 in Fig. 2, which may be standard 1.5 volt dry cells of flashlight size; 6 ohm resistors, indicated at I3 and I3' in Fig. 2, in the battery leads I4 and I4' respectively, and 5 ohm resistors I5 and I5 in the ammeter leads I6 and IB'; milliammeters or other indicators I1 and I'I'; manual switches I8 and I8 in the battery-ground leads I9 and I9'; jacks or terminals and 20 for connecting the lead wires to the primaries of the respective magnetos, and jack 2|- for a common lead wire to ground.` Theface of the meter case may be marked with the letter G to indicate the ground terminal and the letters LM and RM to designate theswitches and jacks for the left and rightmagnetos, respectively; and it will be evident that the meter may be used for testing one magneto at a time by using either of thetwo '.complemental switchesand jacks and the ground terminal,` 2I which is common to the two circuits.

It will be observed that the respective ammeters and batteries are arranged in parallel with their external circuits, and it will be appreciated that the switches I8 and I8' should be left open until the lead wires from the meter box are connected to the magnetos. Otherwise, the meter `needles will uctuate when the switches are closed.

The lead wires to the respective magnetos are indicated at 3| and 3|' in Fig, 2, and the common ground lead is indicated at 32. These leads may be equipped with plugs at one end, tting jacks of the meter case, and their opposite ends may have spring clips for quick attachments of Wires 3| and 3|' to the breaker arms 33 and 33 and of wire 32 to a ground 34 at any metal part of the engine. .The lead wires 3| and 3|' are preferably colored diierently from ground lead 32.

The respective magnetos are represented by the said breaker arms 33 and 33', the points 35 and 35', the coil primaries 36 and 36', andthe condensers 29 and 29 which are common to all such magnetos. It will be understood that the breaker arms are actuated by the cams 3'I and 31', and that the parallel circuits through the breaker points and through the primary are grounded to the engine as indicated at 38 and 38.

Thus, when the lead wires 3|, 3I and 32 are connected as described, and when the switches I 8 and I 8' are then closed, the battery current of the respective meter circuits may ow to ground through any one or more of four parallel paths, three of which are closed and the fourth of which (the breaker points) may be inter- `mittently opened and closed for testing by hand operation of the engine, preferably While the ignition switch is closed.

The circuit through the breaker points offers the line of least resistance when the points are closed. Hence, in that condition, but very little current will ow through the meters and the needle will show a very low reading; the moment the breaker points open, vsubstanwhereas, at,l

tially more current flows through the meters and immediately registers by a jump of the needle to a high reading. This Visual indication ensures that the engine may be accurately timed by adjusting the respective magnetos so that they are synchronized or staggered in operation, as desired. Furthermore, the value of the low reading of the meters tends to indicate the condition of 'the' breaker points, for .if vthe reading higher than normal less current is flowing through the points because they have become pitted or dirty. It Will also be evident that the l improved test meter Wil indicate the internal condition of the magneto, for if its vprimary is open, the indicator -will immediately .show an abnormally high reading while the breaker points are open.

It Will be understood, as aforesaid, that -either test meter of the -device herein disclosed may be used separately, and that a test meter involving a single circuit for vtiming :a single magneto may be constructed and `used in the same fashion :as labove explained Without ydeparting from our invention. It will yalst) appreciated that `other types yof Lelectrical indicator-s, Asuch as bells, buzzersor lightamaybe :utiiized 'ingplace of the ammeters fil or 'N' tonciythe Uobserver them'oment the breaker points open. It is recommended, zhowever, VKthat :anyl'such indicator vor .signal .be lactuated by .a small current; for best "lo Lcapacityvin `said circuit, an indicator sensitive to Weak direct current, and a switch for closing .each circuit independently of the other, the re' 4speciiiye .circuits being connectable in parallel to 'each of a pair of magnetos having a grounded,

uninterrupted'primary and grounded, breaker maints, the container having a common terminal .for a wire leading from the batteries of both test circuits to ground and separate terminals for wires leading from a point in the respective test circuits between the resistor and the indicator Vthereof to `the breaker varms of vthe respective magnetos, lso Ytha1 when v'said wires are -connected and the switches-are closed, each indicator 'shows a rminimum indication While 'the breaker points of 'the `tested magneto are closed, a maximum indication immediately upon the opening of said points, Vand an intermediate vindication 'if the closedpoints -are pittedor idirty.

DONALD F. MCCLELLAN.

CHASENI I 

